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Volume 39 ， Issue 6 ， 2021
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- Abstract：Magnetotactic bacteria (MTB) synthesize intracellular magnetic organelles,magnetosomes,which consist of magnetic crystals that are enveloped in a membrane. Magnetosomes are organized into a chain(s) and confer on cells a magnetic dipolar moment. This magnetic property allows MTB cells to align and swim along geomagnetic field lines,a movement referred to as magnetotaxis. Some MTB species change their swim direction in response to illumination by UV,violet and blue light. Here we analyzed the polarity of morphology,magnetism,and motion in Mediterranean multicellular magnetotactic prokaryotes,also called,magnetoglobules or MMP. The magnetoglobules were assembled from 60–80 cells into an asymmetric ellipsoidal morphology with a relative narrow and large end. They swam dominantly northward,parallel to the direction of the magnetic field,with the narrow-end as the leading side. In response to a reversal in the direction of the magnetic field,they aligned quickly along the magnetic field lines and kept swimming northward. Interestingly,under constant illumination,385-nm UV light,magnetoglobules changed their swimming direction southward anti-parallel to the direction of the magnetic field,with the large-end as the leading side. The change from a northward to southward direction occurred along with an increase of swimming speed. A minimum of 35-mW/cm2 irradiance of UV light was sufficient to trigger the swimming re-orientation. UV radiation also triggered the unidirectional division of magnetoglobules. Together these results revealed a coordination of the polarity of magnetoglobule morphology,magnetic moment,and swimming orientation,in response to magnetic and optical stimuli. The UV triggered the reversal of magnetotaxis and magnetoglobule division indicating the ecological significance of light for multicellular magnetotactic prokaryotes.Keywords：photo-response;magnetic alignment;coordinated swimming7|3|1Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB) are morphologically and phylogenetically diverse prokaryotes commonly able to produce magnetic nanocrystals within intracellular membrane-bound organelles (i.e.,magnetosomes) and to swim along geomagnetic field lines. We studied the diversity of MTB in the samples collected from a mangrove area in the Sanya River,Hainan,South China,using microscopic and microbial phylogenetic methods. Results of microanalysis and observation in microscopy and energy dispersive X-ray spectroscopy (EDXS) reveal a highly morphological diversity of MTB including unicellular cocci,vibrios,rod-shaped bacteria,and three morphotypes of multicellular magnetotactic prokaryotes (MMPs). In addition,analysis of the 16S rRNA gene showed that these MTB were clustered into 16 operational taxonomic units affiliated to the Alpha-,Delta-,and Gamma-proteobacteria classes within the Proteobacteria phylum. Meanwhile,by using the coupled fluorescence and transmission electron microscopy analysis,rodshaped bacteria,vibrio,and cocci were phylogenetically and structurally identified at the single-cell level. This study demonstrated highly diverse MTB communities in the mangrove ecosystem and provide a new insight into the overall diversity of MTB.Keywords：magnetotactic bacteria;diversity;magnetosome;phylogenetic analysis;coordinated fluorescence in-situ hybridization transmission electron microscopy (FISH-TEM);mangrove5|5|1Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB) are a group of microorganisms capable of orientating and swimming along magnetic fields because they contain intracellular biomineralized magnetosomes composed of magnetite (Fe3O4) or/and greigite (Fe3S4). They are ubiquitous in freshwater,brackish,and marine habitats,and are cosmopolitan in distribution. However,knowledge of their occurrence and distribution in seamount ecosystems is limited. We investigated the diversity and distribution of MTB in the Caroline Seamount (CM4). The abundance of living MTB in 12 stations in depth varying from 90 to 1 545 m was 1.1×103-43.7×103 inds./dm3. Despite diverse shapes of MTB observed,magnetotactic cocci were the dominant morphotype and could be categorized into two types: 1) typical cocci that appeared to have peritrichous flagella; and 2) those characterized by having a drop-shaped form and one bundle of flagella located at the thin/narrow end of the cell. Transmission electron microscopy (TEM) analysis revealed that the magnetosomes formed by those magnetotactic cocci are magnetite (Fe3O4) with octahedral crystal habit. A total of 41 operational taxonomic units (OTUs) of putative MTB (2 702 reads) were acquired from nine stations,based on high-throughput sequencing. Of these,40 OTUs belonged to the Proteobacteria phylum and one belonged to the Nitrospirae phylum. We found apparent connectivity between the MTB populations on the Caroline and Kexue (Science in Chinese) seamounts,although the diversity of MTB on Caroline was much richer than on the Kexue Seamount. Our results imply that the unique topography of seamounts and other as-yet unclear environmental factors could lead to evolution of different flagella arrangements in magnetotactic cocci,and the occurrence of octahedral magnetite magnetosomes.Keywords：magnetotactic bacteria;Caroline seamount;abundance;diversity;magnetosome4|2|1Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB),ubiquitous in soil and fresh and saltwater sources have been identified in the microbiome of humans and many animals. MTB endogenously produce magnetic nanocrystals enabling them to orient and navigate along geomagnetic fields. Similar magnetite deposits have been found throughout the tissues of the human brain,including brain regions associated with orientation such as the cerebellum and hippocampus,the origins of which remain unknown. Speculation over the role and source of MTB in humans,as well as any association with the brain,remain unanswered. We performed a metagenomic analysis of the gut microbiome of 34 healthy females as well as grey matter volume analysis in magnetite-rich brain regions associated with orientation and navigation with the goal of identifying specific MTB that could be associated with brain structure in orientation and navigation regions. We identified seven MTB in the human gut microbiome: Magnetococcus marinus,Magnetospira sp. QH-2,Magnetospirillum magneticum,Magnetospirillum sp. ME-1,Magnetospirillum sp. XM-1,Magnetospirillum gryphiswaldense,and Desulfovibrio magneticus. Our preliminary results show significant negative associations between multiple MTB with bilateral flocculonodular lobes of the cerebellum and hippocampus (adjusted for total intracranial volume,uncorrected P < 0.05). These findings indicate that MTB in the gut are associated with grey matter volume in magnetite-rich brain regions related to orientation and navigation. These preliminary findings support MTB as a potential biogenic source for brain magnetite in humans. Further studies will be necessary to validate and elucidate the relationship between these bacteria,magnetite concentrations,and brain function.Keywords：magnetotactic bacteria;human microbiome;microbiota-gut-brain axis;magnetoreception5|2|0Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB) are a group of prokaryotes having the ability to orient and swim along geomagnetic field lines because they contain intracellular magnetosomes that are synthesized through a biomineralization process. Magnetosomes have recently also been found in unicellular eukaryotes,which are referred to as magnetically responsive protists (MRPs). The magnetosomes have three origins in MRPs. In this study,we characterized a MTB-grazing ciliated MRP that was magnetically collected from intertidal sediment of Huiquan Bay,Qingdao,China. Based on 18S rRNA gene sequence analysis,the ciliated MRP was tentatively identified as Uronemella parafilificum HQ. Using transmission electron microscopy,we observed that magnetosomes having 2–3 shapes were randomly distributed within this ciliate. Energydispersive X-ray spectroscopy and high-resolution transmission electron microscopy images of the magnetosomes were consistent with them being composed of magnetite. Magnetosomes having the same shape and mineral composition were also detected in MTB that occurred in the same environment as the ciliated MRP. Statistical analysis showed that the size and shape of the magnetosomes in the ciliated MRP were similar to those in MTB. The results suggest that this ciliated MRP can graze,ingest,and digest various types of MTB. It is certainly worth noting that this is the first record of MRPs in Asian aquatic sediment and suggesting they might be widely distributed. These results also support the assertion that MRPs probably contribute to the ecological cycles of iron,and expand possibilities for research into the mechanism of magnetoreception in eukaryotes.Keywords：magnetically responsive protist;ciliate;magnetotactic bacteria;magnetosome;graze;magnetoreception5|3|2Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB) are ubiquitous prokaryotes that orient along magnetic field lines due to magnetosomes' biomineralization within the cell. These structures are ferrimagnetic organelles that impart a magnetic moment to the cell. To succeed in producing magnetosomes,MTB accumulate iron in (i) cytoplasm; (ⅱ) magnetosomes; and (ⅲ) nearby the organelle. It has already been estimated that a single MTB has an iron content of 10 to 100-fold higher than Escherichia coli. Phages are the most abundant entity in oceans and are known for controlling nutrient flow such as carbon and nitrogen by viral shunt and pump. The current work addresses the putative role of phages that infect MTB on the iron biogeochemical cycle. Can phage infection in MTB hosts cause a biogenic iron fertilization-like event in localized microenvironments? Are phages critical players in driving magnetosome biomineralization genes (BGs) horizontal transfer? Further investigation of those events,including frequency of occurrence,is necessary to fully comprehend MTB's effect on iron cycling in aqueous environments.Keywords：horizontal gene transfer;iron biogeochemical cycle;magnetotactic bacteria;magnetosome biomineralization genes;phages4|2|0Updated：2023-05-20
- Abstract：Magnetotactic bacteria can orientate in the Earth's magnetic field to search for their preferred microoxic environments, which is achieved by their unique organelles, the magnetosomes. Magnetosomes contain nanometer-sized crystal particles of magnetic iron minerals, which are only synthesized in lowoxygen environments. Although the mechanism of aerobic repression for magnetosome biomineralization has not yet fully understood, a series of studies have verified that redox modulation is pivotal for magnetosome formation. In this review, these advances in redox modulation for magnetosome biosynthesis are highlighted, mainly including respiration pathway enzymes, specific magnetosome-associated redox proteins, and oxygen- or nitrate-sensing regulators. Furthermore, their relationship during magnetosome biomineralization is discussed to give insight into redox control and biomineralization and inspire potential solutions for the application of respiration pathways to improve the yields of magnetosome.Keywords：magnetotactic bacteria;magnetosome;biomineralization;respiration;redox control4|2|1Updated：2023-05-20
- Abstract：Based on analysis of gene structure of mamXY operon in Magnetospirillum gryphiswaldense strain MSR-1, we constructed a mamZ deletion mutant strain (∆mamZ) and four complemented strains with different mamZ fragment lengths. Various cell phenotypic and physiological parameters were evaluated and compared among the wild-type (WT), mutant, and complemented strains. Cell growth rates were not notably different; however, magnetic response (Cmag) and iron uptake ability were significantly lower in ∆mamZ. High-resolution transmission electron microscopy (HR-TEM) showed that magnetosomes in ∆mamZ were small and irregular, and rock magnetic measurements suggested that they contained immature particles. In comparison to WT of MSR-1, intracellular iron content of ∆mamZ and the complemented strains cultured with 20 μmol/L iron source was similar or slightly higher. The complemented strains were unable to synthesize mature or normal amounts of magnetosomes, apparently because of abnormal expression of the transmembrane domain of MamZ protein. Real-time reverse transcription polymerase chain reaction (RTqPCR) analysis showed that relative transcription levels of mamX and ftsZ-like genes in ∆mamZ were higher at 18 h than at 12 h, suggesting that MamXY proteins play cooperative functional roles in the magnetosome maturation process. Transcription level of mms6 was significantly upregulated in ∆mamZ (incubated at 12 h) and the complemented strains (incubated at 12 and 18 h), reflecting possible interaction between MamXY and Mms6 proteins during magnetosome biosynthesis. These findings, taken together, demonstrate the essential role of MamZ in the magnetosome maturation process in MSR-1.Keywords：Magnetospirillum gryphiswaldense;mamZ;deletion;mamXY operon;magnetosome maturation4|0|0Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB) display magnetotaxis ability because of biomineralization of intracellular nanometer-sized, membrane-bound organelles termed magnetosomes. Despite having been discovered more than half a century, only a few representatives of MTB have been isolated and cultured in the laboratory. In this study, we report the genomic characterization of a novel marine magnetotactic spirillum strain SH-1 belonging to the genus Terasakiella that was recently isolated. A gene encoding haloalkane dehalogenase, which is involved in the degradation of chlorocyclohexane, chlorobenzene, chloroalkane, and chloroalkene, was identified. SH-1 genome contained cysCHI and soxBAZYX genes, thus potentially capable of assimilatory sulfate reduction to H2S and using thiosulfate as electron donors and oxidizing it to sulfate. Genome of SH-1 also contained genes encoding periplasmic dissimilatory nitrate reductases (napAB), assimilatory nitrate reductase (nasA) and assimilatory nitrite reductases (nasB), suggesting that it is capable of gaining energy by converting nitrate to ammonia. The pure culture of Terasakiella sp. SH-1 together with its genomic results offers new opportunities to examine biology, physiology, and biomineralization mechanisms of MTB.Keywords：magnetotactic bacteria;magnetotaxis;pure culture;comparative genomic analysis4|2|1Updated：2023-05-20
- Abstract：Magnetotactic bacteria are capable of biosynthesizing magnetic nanoparticles, also called magnetosomes, and swimming along magnetic field lines. The abilities endow the whole cells of magnetotactic bacteria with such applications as targeted therapy and manipulation of microrobots. We have shown that the intact marine magnetotactic bacteria MO-1 kill efficiently antibiotic-resistant pathogen Staphylococcus aureus in vivo, but the biocompatibility of this marine bacterium is unknown. In this study, the strain MO-1 was chosen to analyze its biocompatibility and potential for biomedicine applications. Results showed that MO-1 cells could be guided at 37 ℃ under an external magnetic field and swim in the blood plasma and urine. They could keep active locomotivity within 40 min in the plasma and urine, although their velocity slowed down. When incubated with human cells, magnetotactic bacteria MO-1 had no obvious effects on cellular viability at low dose, while the cell toxicity increased with the augmentation of the quantity of the MO-1 cells added. In the in-vivo experiments, the median lethal dose of magnetotactic bacteria MO-1 in rats was determined to be 7.9×1010 bacteria/kg. These results provided the foundation for the biocompatibility and safety evaluations of magnetotactic bacteria MO-1 and suggested that they could be basically used in clinical targeted therapy.Keywords：magnetotactic bacteria;motility;cell interaction;median lethal dose4|3|2Updated：2023-05-20
- Abstract：Magnetotactic bacteria (MTB) intact cells have been applied in magnetic hyperthermia therapy of tumor, showing great efficiency in heating for tumor cell inhibition. However, the detailed magnetic hyperthermia properties and optimum heat production conditions of MTB cells are still poorly understood due to lack of standard measuring equipment. The specific absorption rate (SAR) of MTB cells is often measured by home-made equipment at a limited frequency and magnetic field amplitude. In this study, we have used a commercial standard system to implement a comprehensive study of the hyperthermic response of Magnetospirillum gryphiswaldense MSR-1 strain under 7 frequencies of 144–764 kHz, and 8 field amplitudes between 10 and 45 kA/m. The measurement results prove that the SAR of MTB cells increases with magnetic field frequency and amplitude within a certain range. In combination with the magnetic measurements, it is determined that the magnetic hyperthermia mechanism of MTB mainly follows the principle of hysteresis loss, and the heat efficiency of MTB cells in alternating magnetic field are mainly affected by three parameters of hysteresis loop, saturation magnetisation, saturation remanent magnetisation, and coercivity. Thus when we culture MTB in LA-2 medium containing sodium nitrate as source of nitrogen, the SAR of MTBLA-2 cells with magnetosomes arranged in chains can be as high as 4 925.6 W/g (in this work, all SARs are calculated with iron mass) under 764 kHz and 30 kA/m, which is 7.5 times than current commercial magnetic particles within similar size range.Keywords：magnetotactic bacteria (MTB);hyperthermia;rock magnetism;alternating magnetic field (AMF)4|4|0Updated：2023-05-20
Special Section: Magnetotactic Bacteria and Magnetoreception
- Abstract：Traditionally, the estimated volume transport of the North Equatorial Current/Undercurrent (NEC/NEUC) is based on geostrophic equations and/or model results; however, direct observational evidence has not been acquired. We focused on one-year mooring observation data collected along 130°E and calculated the NEC/NEUC volume transport and explore its variability. Results show that the mean NEC and NEUC volume transports calculated from the mean velocity structures in the upper 950 m are 39 Sv and 6 Sv, respectively. Analysis of daily mooring data indicated that the volume transport of the NEC is approximately 52 (±14) Sv and the volume transport of the NEUC is approximately 18 (±13) Sv. A significant 40-day variation existed for the volume transport of both the NEC and NEUC. Overall, the intraseasonal variability of the NEC is vertically coherent with that of the NEUC. Observations indicated that the NEUC has three cores centered at approximately 8.5°N (~500 m), 12.5°N (~700 m), and 17.5°N (~900 m), of which the middle core (12.5°N) is the strongest. The 40-day variability of the NEC and NEUC is related to the variability of local wind stress curl anomalies among various Madden‐Julian Oscillation phases. When local wind field generates a negative (positive) wind stress curl anomaly, a weaker NEC (NEUC) and stronger NEUC (NEC) would occur.Keywords：intraseasonal variability (ISV);North Equatorial Current/Undercurrent (NEC/NEUC);transport;Madden-Julian Oscillation (MJO)5|2|0Updated：2023-05-20
- Abstract：Velocity vertical profiles in the bottom boundary layer are important to understand the oceanic circulation. The logarithmic vertical profile, u=Alnz+B, is the universal profile for the horizontal velocity in the boundary layer, in which two coefficients (A and B) need to be determined. The two coefficients are the functions of the friction velocity (u*) and the roughness length (z0), and they are calculated using u* and z0. However, the measurement of u* and z0 is a challenge. In the present study, an approach is developed to estimate the two coefficients (A and B) by using a series of flume laboratory experiments with flat boundary and regularly distributed cylinders as the rough boundaries. An acoustic doppler velocimeter (ADV) is used to measure the velocity vertical profiles of the steady flow. Using the measured velocity data, the regressed logarithmic profiles are obtained. Based on the series of the A and B values, the mathematical formula for A and B are statistically established as the function of the cylinder height, inflow velocity, and the water depth, which avoids the measurement of the friction velocity and the roughness length.Keywords：velocity vertical logarithmic distribution;bottom boundary layer;the friction velocity4|2|0Updated：2023-05-20
- Abstract：The Kuroshio Extension (KE) is one of the most eddy-energetic regions in the global ocean. However, most mesoscale eddy studies in the region are focused on surface eddies and the structure and characteristics of three-dimensional (3-D) eddies require additional research. In this study, we proposed a 3-D eddy identification and tracking algorithm based on pressure anomalies, similar to sea level anomalies (SLAs) for surface eddy identification. We applied this scheme to a 5-year (2008–2012) high-resolution numerical product to develop a 3-D eddy dataset in the KE. The reliability of the numerical product was verified by the 5-year temperature/salinity hydrological characteristics and surface eddy distribution. According to the 3-D eddy tracking dataset, the number of eddies decreased dramatically as the eddy existence-time increased and more anticyclonic eddies (AEs) had an existence-time longer than 1 week than cyclonic eddies (CEs). We presented daily variations in the 3-D structure of two 3-D eddy-tracking trajectories that exhibit a certain jump in depth and a shift toward the west and equator. In addition to the bowl, lens, and cone eddies that have been discovered by previous researchers, we found that there is a cylindrical eddy, and its eddy radii are almost consistent across all layers. CEs cause significant negative temperature anomalies, "negative-positive" salinity anomalies, and sinking current fields in the KE region, while AEs cause positive temperature anomalies, "positive-negative" salinity anomalies, and upward current fields. The four types of eddies have different effects on the temperature/salinity anomalies and current field distribution which are related to their structure.Keywords：mesoscale eddy;pressure anomalies;three-dimensional structure;identification;tracking4|3|3Updated：2023-05-20
- Abstract：We present observations from deployments of turbulent microstructure instrument and CTD package in the northern South China Sea from April to May 2010. From them we determined the turbulent mixing (dissipation rate ε and diapycnal diffusivity κ), nutrients (phosphate, nitrate, and nitrite), nutrient fluxes, and chlorophyll a in two transects (A and B). Transect A was located in the region where turbulent mixing in the upper 100 m was weak (κ~10-6–10-4 m2/s). Transect B was located in the region where the turbulent mixing in the upper 100 m was strong (κ~10-5–10-3 m2/s) due to the influence of internal waves originating from the Luzon Strait and water intrusion from the Western Pacific. In both transects, there was a thin subsurface chlorophyll maximum layer (SCML) (> 0.25 mg/m3) nested in the upper 100 m. The observations indicate that the effects of turbulent mixing on the distributions of nutrients and chlorophyll a were different in the two transects. In the transect A with weak turbulent mixing, nutrient fluxes induced by turbulent mixing transported nutrients to the SCML but not to the upper water. Nutrients were sufficient to support a local SCML phytoplankton population and the SCML remained compact. In the transect B with strong turbulent mixing, nutrient fluxes induced by turbulent mixing transported nutrients not only to the SCML but also to the upper water, which scatters the nutrients in the water column and diffuses the SCML.Keywords：turbulent mixing;diapycnal diffusivity;nutrients;nutrient flux;chlorophyll a4|0|1Updated：2023-05-20
Physics
- Abstract：Sea surface wind (SSW) observations from a newly developed "Black Pearl" wave glider, the Chinese-French Oceanography Satellite (CFOSAT), the HY-2A microwave scatterometer, and a recently released high-resolution atmospheric reanalysis (ERA5) are evaluated with respect to in-situ buoy observations (115.46°E, 19.85°N) from the South China Sea. Buoy observations from June to November 2019 are used to evaluate the wind estimates from the different platforms. The comparisons show that the HY-2A and CFOSAT scatterometer wind speeds have mean root mean square errors (RMSEs) of approximately 1.6 and 1.6 m/s, respectively, and the corresponding mean wind direction RMSEs are approximately 19° and 17°, which indicates that these satellite retrievals meet the requirements of design engineering missions. The wind speed and wind direction RMSEs of ERA5 are approximately 1.9 m/s and 33°, respectively. The correlation coefficients between the HY-2A, CFOSAT, and ERA5 wind speeds and the buoy observations are 0.86, 0.85, and 0.84, respectively, and the corresponding coefficients of the wind direction are 0.98, 0.98, and 0.93, respectively, at a 95% confidence level. However, the wind sensor in the wave glider provides relatively poor-quality observations compared with the buoy measurements and has higher wind speed and wind direction RMSEs of 2.9 m/s and 50.1°, respectively. Taylor diagrams are utilized to illustrate comprehensive wind comparisons between the multiplatform observations and buoy observations. The results help identify the basic biases in SSWs among different products and enhance confidence in the future use of SSW data for studies of upper ocean dynamics and climate analysis. Suggestions are also offered to help improve the design of next-generation wave gliders.Keywords：sea surface wind (SSW);calibration;South China Sea (SCS);wave glider;fifth European Centre for Medium-Range Weather Forecasts reanalysis (ERA5);HY-2A;Chinese-French Oceanography Satellite (CFOSAT)4|2|1Updated：2023-05-20
- Abstract：The Andaman Sea has been a classic study region for internal solitary waves (ISWs) for several decades, and extraordinarily large ISWs are characteristic of the Andaman Sea in the Indian Ocean. This paper presents results on the estimation of the propagation velocity of ISWs in the Andaman Sea that were tracked using 195 image pairs acquired by MODIS National Aeronautics and Space Administration (NASA) Terra/Aqua satellites between January 2014 and December 2018. A total of 562 ISWs were identified during the period, and the results of the propagation velocity distribution of ISWs in the Andaman Sea are presented. The estimated propagation velocity of ISWs agrees well with the theoretical results derived from the Korteweg-de Vries (KdV) equation using monthly climatology stratification data and local bathymetry. The ISW propagation velocity decreases as they propagate from deep to shallow water; the maximum propagation velocity of 3.27 m/s was estimated on the western side of the Nicobar Islands and minimum speed of 0.54 m/s occurred in the shallow water region of the southeastern Andaman Sea. The results show that the ISW propagation characteristics differ in the northern, central, and southern regions of the Andaman Sea. In the northern Andaman Sea, the velocity of ISWs propagating westward was greater than that of ISWs propagating eastward at the same water depth. In the central Andaman Sea, the propagation velocity of the ISWs differed over a small area at a depth of 2 500 m, and the velocity of ISWs in the deep mixing layer in winter was higher than that in the shallow mixing layer in spring. Monthly variations in ISW propagation velocity were analyzed in the southern Andaman Sea, and the velocity of ISWs differed greatly in shallow water and was not significantly different in deep water. Water depth and monthly stratification play vital roles in controlling the phase speed of ISWs in the Andaman Sea. This study will provide a basis for the propagation and prediction of ISWs in the Andaman Sea.Keywords：internal solitary waves;propagation velocity;remote sensing;Andaman Sea4|3|5Updated：2023-05-20
- Abstract：231Pa and 230Th are two crucial isotopes in the ongoing GEOTRACES Project. However, the controversy on 231Pa/230Th proxy pertaining to archiving ocean circulation or recording paleoproductivity, is still unresolved, partly owing to the unclear understanding of fractionation between 231Pa and 230Th during adsorption. In this study, controlled experiments were conducted to examine the adsorption of 234Th and 233Pa onto biogenic particles (SiO2 and CaCO3), authigenic minerals (MnO2 and Fe2O3), and lithogenic minerals (kaolinite, attapulgite, montmorillonite, and aluminum oxyhydroxides), and the role of organic compounds in regulating the adsorption of 234Th and 233Pa in natural seawater was evaluated. The distribution coefficients (Kd, presented as logKd) varied from 3.56 to 6.05 and from 3.27 to 5.82 for 234Th and 233Pa, respectively. Fe2O3 is the strongest sorbent for both 234Th and 233Pa. Most of the particles showed comparable logKd values for either 234Th (~4.8) or 233Pa (~3.9) in the presence of dextran, indicating that the adsorption of Th and Pa is likely controlled by organic coating on particle surfaces. The fractionation factors (FTh/Pa) of SiO2 (3±1) and CaCO3 (33±1) suggest in situ observed preferential scavenging of 230Th to 231Pa in the surface water of low- to mid-latitude regions and the nearly equal removal in the Antarctic Ocean where biogenic silica dominates the particle regime. The FTh/Pa values of the lithogenic and biogenic particles indicate that 230Th is scavenged prior to 231Pa in the particle-scarce ocean interior. The equal scavenging of 230Th and 231Pa at the ocean margins and the ridge crests is dominated by high particle fluxes instead of particle composition control. These results imply that 230Th/231Pa can be used as different proxies in different oceanic settings.Keywords：thorium;protactinium;paleoproductivity;circulation;particle dynamics4|2|0Updated：2023-05-20
Chemistry
- Abstract：Hydrozoans and anthozoans are an important component of a great variety of marine communities, particularly abundant and ubiquitous as part of the fouling assemblages around the globe. Several negative impacts have been associated to their occurrence on artificial substrata. In the coastal waters of China, a total of 76 species of fouling cnidarians were observed and classified. According to the occurrence frequency or biomass, the major species in the Bohai and Yellow Seas were Ectopleura marina, Bougainvillia sp., and Eudendrium capillare; in the East China Sea Anthopleura nigrescens, Diadumene lineata, and Ectopleura crocea; and in the South China Sea Clytia sp., Obelia sp., and Actiniaria spp. The peak period of settlement of most species was mainly in summer and autumn. With the decrease of latitude, species number increased greatly and even cnidarian fouling was observed all year round in the East and South China Seas. Salinity was another factor affecting species distribution. Naturally, immersion time of substrata also directly affects the characteristics of cnidarians in fouling communities.Keywords：hydrozoan;anthozoan;biofouling;distribution;settlement4|2|1Updated：2023-05-20
- Abstract：Harmful algal bloom (HAB) is an ecological disaster to local mariculture. At present, its impact on macrophytes has not been well studied. In this study, we cultivated sexually propagated embryos of Sargassum fusiformis— an edible seaweed—in Prorocentrum donghaiense suspensions at different cell densities (0, 0.50×105, 0.75×105, 1.00×105, and 1.50×105 cells/mL) for 10 days, during which growth and photosynthetic activities of the embryos were determined, and a monocultivation was set up for comparison. Results show that the relative growth rate and photosynthetic activities of the embryos co-cultivated with P. donghaiense were inhibited mostly and significantly in the cell densities of 0.75×105, 1.00×105, and 1.50×105 cells/mL, and the inhibitory effects increased in overall with increased cell densities. The maximum relative electron transport rates (rETRmax) and apparent photosynthetic efficiency (α) of co-cultivated embryos were all significantly lower than monocultivation ones on the 10th day. Furthermore, the photosynthetic activity detected by chlorophyll-a fluorescence transient (i.e., OJIP), the electron transport among electron transfer accepters of PSⅡ (photosystem Ⅱ) and that from PSⅡ to PSI (photosystem Ⅰ) was restricted, which is probably responsible for the decreases of rETRmax and α in the co-cultivated embryos. In addition, parts of the photosynthetic reaction centers of PSⅡ in the co-cultivated embryos were inactivated. Therefore, P. donghaiense bloom could restrain the development and photosynthetic activities of S. fusiformis embryos, reduce the seedlings stock, and eventually hinder the development of S. fusiformis production industry.Keywords：embryo;JIP-test;photosynthesis;Prorocentrum donghaiense;Sargassum fusiformis;harmful algal bloom4|0|0Updated：2023-05-20
- Abstract：Large-scale green tides in the Yellow Sea occurred for 13 consecutive years since 2007. The unusual co-occurrence of green tides and golden tides occurred in the Yellow Sea in 2017. The causative species are Ulva prolifera and/or Sargassum horneri. Previous studies on physiological response characteristics of U. prolifera and S. horneri are done in the laboratory mainly, and there is no in-situ comparative study in this regard. In this study, the in-situ physiological response characteristics of both species were measured. The results indicated that cyclic electron flow and antioxidant system play more important roles in protecting U. prolifera, while non-photochemical quenching is more important for adapting to the environment in S. horneri. U. prolifera has a stronger ability to utilize nutrients to rapidly increase its biomass under a suitable condition compared to S. horneri.Keywords：Ulva prolifera;Sargassum horneri;environmental response strategy;in-situ study4|0|0Updated：2023-05-20
- Abstract：Conspecific seagrass living in differing environments may develop different root system acclimation patterns. We applied X-ray computed tomography (CT) for imaging and quantifying roots systems of Zostera japonica collected from typical oligotrophic and eutrophic sediments in two coastal sites of northern China, and determined sediment physicochemical properties that might influence root system morphology, density, and distribution. The trophic status of sediments had little influence on the Z. japonica root length, and diameters of root and rhizome. However, Z. japonica in oligotrophic sediment developed the root system with longer rhizome node, deeper rhizome distribution, and larger allocation to below-ground tissues in order to acquire more nutrients and relieve the N deficiency. And the lower root and rhizome densities of Z. japonica in eutrophic sediment were mainly caused by fewer shoots and shorter longevity, which was resulted from the more serious sulfide inhibition. Our results systematically revealed the effect of sediment trophic status on the phenotypic plasticity, quantity, and distribution of Z. japonica root system, and demonstrated the feasibly of X-ray CT in seagrass root system research.Keywords：Zostera japonica;root system;acclimation pattern;sediment;trophic status;X-ray computed tomography5|0|0Updated：2023-05-20
- Abstract：Obvious spatiotemporal heterogeneity is a distinct characteristic of ecosystems in subtropical bays. To aid targeted management and ecological restoration in long and narrow semi-enclosed subtropical bays, we analyzed seasonal and regional differences in long-term changes (1980–2019) in the biomass and abundance of large mesozooplankton (LMZ; >505 μm) in Xiangshan Bay, Zhejiang, China. We found spatiotemporal heterogeneity in the historical changes of LMZ. Significant negative trends in LMZ biomass were found in the inner and middle bay during the warm season (summer and autumn), when the nutrient concentration (especially dissolved inorganic nitrogen) and temperature increased simultaneously. Nutrient changes in Xiangshan Bay began in the late 1980s or early 1990s, coinciding with large-scale fish cage development. A rapid decline in LMZ biomass occurred after 2005 when power plants commenced operation, accelerating the warming trend. Therefore, the joint stress of eutrophication and warming likely precipitated the decline in LMZ biomass. Conversely, a significant increase in LMZ biomass was found in the outer bay in spring. This trend was consistent with the trend of LMZ biomass near the Changjiang (Yangtze) River estuary, which indicates that the pelagic ecosystem in the outer bay was affected by water from the Changjiang River estuary during spring. Based on our results, ecosystem management and restoration in semi-enclosed subtropical bays should focus on internal waters, which have a poor capacity for water exchange. For Xiangshan Bay, the changes in the Changjiang River estuary ecosystem during the cold season (winter and spring) should also be considered.Keywords：large mesozooplankton;long-term changes;spatiotemporal heterogeneity;Xiangshan Bay6|3|0Updated：2023-05-20
Ecology
- Abstract：Sea cucumbers are echinoderm species with a leathery skin and an elongated body. Natural compounds, including saponins, have been previously isolated from sea cucumber. The majority of saponins derived from this organism typically belong to the triterpene glycosides, which exhibit various biological effects (e.g., antifungal, cytotoxic, hemolytic, and cytostatic immunomodulatory activities). In the present study, 30 saponin biosynthesis enzymes, namely 2 AACTs, 2 FPSs, 2 HMGSs, 2 OSCs, 1 SS, 2 SEs, and 19 UGTs, were found in the genome of sea cucumber Apostichopus japonicus. Compared with upstream saponin biosynthesis enzymes (i.e., AACTs, FPSs, HMGSs, OSCs, and SSs), the downstream saponin biosynthesis enzymes (SEs and UGTs) shared lower amino acid sequence similarity with the corresponding genes in other echinoderms. It was proposed that the enzyme structures comprised both α-helices and β-sheets. Notably, only a low percentage of β-sheets were present in FPSs, OSCs, and SS. The saponin biosynthesis enzymes showed dynamic expression patterns during five critical developmental stages of A. japonicus (fertilized oocytes, blastula, gastrula, doliolaria, and penractula). The present study involved elucidation of putative saponin biosynthesis pathways in sea cucumber and provides a valuable platform for further investigation of saponin biosynthesis in echinoderms.Keywords：triterpene saponin biosynthesis;sea cucumber;enzyme;expression;development4|3|1Updated：2023-05-20
- Abstract：Seahorses have evolved many unique biological traits, including a male brood pouch, the absence of caudal and pelvic fins, and the lack of spleen and gut-associated lymphatic tissue. The mitogenactivated protein kinases (MAPKs) are known to be involved in various important biological processes including growth, differentiation, immunity, and stress responses. Therefore, we hypothesized that the adaptive evolution and expression of the MAPK gene family in seahorse may differ from those of other teleost species. We identified positive selection sites in the erk2, erk5, jnk1, and p38α MAPK genes of the lined seahorse Hippocampus erectus and tiger-tailed seahorse Hippocampus comes. A novel expression profile of MAPK cascade genes was found in seahorse larvae during the first day after birth based on the RNA-seq data of H. erectus, which reflected vital signs of immune response to its parental immune system. The expression patterns of the four positively selected MAPK genes were analyzed following the bacterial challenge of Vibrio fortis, revealing their upregulation pattern in brood pouch and other immune tissues. This study enriched our knowledge of the evolution of the H. erectus MAPK subfamilies, and could help better understanding the functional role of MAPKs in teleosts.Keywords：mitogen-activated protein kinases (MAPKs);Hippocampus erectus;genomic structure;positive selection;immune regulation4|0|1Updated：2023-05-20
- Abstract：The homodimeric kinesin-2 protein KIF17 functions in intracellular transport and spermiogenesis in mammals. However, its role in fish spermiogenesis has not been reported. Here, we aimed to clone full-length kif17 cDNA and determine the molecular characteristics and expression patterns of KIF17 in Larimichthys polyactis spermiogenesis. The full-length cDNA of L. polyactis kif17 (Lp-kif17) was sequenced and found to contain a 332-bp 5' untranslated region, 480-bp 3' untranslated region, and 2 433-bp open reading frame encoding 810 amino acids. Bioinformatics analyses showed that L. polyactis KIF17 (Lp-KIF17) shared high sequence similarity with homologs in other animals and possessed an N-terminal motor domain with microtubule-binding sites and adenosine triphosphate (ATP) hydrolysis sites, a stalk domain containing two coiled-coil regions, and a C-terminal tail domain. The Lp-kif17 mRNA was widely expressed in various tissues, with the highest level in the brain, followed by that in the testis. Fluorescence in situ hybridization (FISH) analysis revealed that Lp-kif17 was continuously expressed in spermiogenesis, showing that it had potential functions in this process. Using immunofluorescence (IF) analysis, we found that Lp-KIF17 colocalized with tubulin and was transferred from the perinuclear cytoplasm to the side of spermatid where the tail forms during spermiogenesis. These findings suggested that KIF17 is involved in L. polyactis spermiogenesis. In particular, it may participate in nuclear shaping and tail formation by interacting with perinuclear microtubules during spermatid reshaping. In addition to providing evidence for the role of KIF17 in fish spermatid reshaping, this study provides important data for studies of reproductive biology in L. polyactis.Keywords：KIF17;spermiogenesis;Larimichthys polyactis;spermatid reshaping4|0|0Updated：2023-05-20
- Abstract：Salt stress is an abiotic stress to plants in especially saline lakes. Dunaliella, a halophilic microalga distributed throughout salt lakes and seas, can respond to different salinity stresses by regulating the expression of some genes. However, these genes and their function and biological processes involved remain unclear. Profiling these salt-stress-related genes in a high-salt-tolerant Dunaliella species will help clarify the salt tolerance machinery of Dunaliella. Three D. salina_YC salt-stress groups were tested under low (0.51 mol/L), moderate (1.03 mol/L), and high (3.42 mol/L) NaCl concentrations and one control group under very low (0.05 mol/L) NaCl concentration and 3 transcriptome results that were deep sequenced and de novo assembled were obtained per group. Twelve high-quality RNA-seq libraries with 46 585 upregulated and 47 805 downregulated unigenes were found. Relative to the control, 188 common differentially expressed genes (DEGs) were screened and divided into four clusters in expression pattern. Fifteen of them annotated in the significant enriched Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were validated via qPCR. Their qPCR-based relative expression patterns were similar to their RNA-seq-based patterns. Two significant DEGs, the geranylgeranyl diphosphate synthase coding gene (1 876-bp cDNA) and diacylglycerol O-acyltransferase coding gene (2 968-bp cDNA), were cloned and analyzed in silico. The total lipid content, superoxide dismutase specific activity, and betacarotene content of D. salina_YC increased gradually with increasing salinity. In addition, the expression of 11 validated genes involved in fatty acid biosynthesis/degradation, active oxygen or carotenoid metabolisms showed significant changes. In addition, algal photochemical efficiency was diminished with increasing salinity, as well as the expression of 4 photosynthesis-related genes. These results could help clarify the molecular mechanisms underlying D. salina responses to the Yuncheng Salt Lake environment and lay a foundation for further utilization of this algal resource.Keywords：Dunaliella salina;transcriptome analysis;de novo assembly;salt stress4|0|1Updated：2023-05-20
- Abstract：A new species Lobophora tsengii is described from Bach Long Vy (Bailongwei) Island, Haiphong Province, Vietnam. The plants inhabit the subtidal zone and have predominantly erect fan-shaped thalli that attach to the substrate by a basal holdfast. The thallus is commonly composed of a single layer of large medullary cells with four layers of cortical cells on either side of the medulla. The newly collected specimens from the island are morphologically similar to those from Hainan Island, China, but differ from the New Caledonian ones in having thicker thallus. In molecular phylogenetic analyses based on concatenated rbcL and cox3 s equences, the specimens from the island were 100% identical to those from Hainan Island, China, and they formed a clade separating from other Lobophora species. Additionally, based on analyses of numerous cox3 s equences, our specimens were also distinguished from the closely related taxa occurring in New Caledonia, Kenya, and West Australia. Combining the morphological and molecular analyses, we conclude that our specimens represent a new species of Lobophora, which is apparently endemic to the Beibu Gulf (Gulf of Tonkin) and adjacent waters.Keywords：Bach Long Vy (Bailongwei) Island;cox3;Lobophora;molecular phylogeny;morphology;rbcL4|0|0Updated：2023-05-20
- Abstract：The genus Neglectella Vodenicarov & Benderliev has a morphology similar to the well-known genus Oocystis, except for the numerous chloroplasts stacked in the surface layer of the cell. Neglectella subsequently experienced complex taxonomy changes with members being transferred in and out, and five species are now accepted. In this study, a new alga with morphology corresponding to this genus was collected in China and successfully cultured in laboratory. Morphological observations in light microscopy and transmission electronic microscopy (TEM) and phylogenetic analyses revealed that it is a new species, described here as Neglectella glomerata sp. nov. It differed from other Neglectella species due to a morphological difference in its unique mucilaginous colony with a large number of cells, multiple pyrenoids in each chloroplast, smaller cell size, and more elongated cell shape. Phylogenetic analyses placed this alga in the subfamily Eremosphaeroideae of the family Oocystaceae and showed its close relationship with Neglectella peisonis. Further morphological comparisons combined with phylogenetic results revealed three different morphological types in Neglectella. The new type represented by our new species may represent a transitional morphology in intermediate taxonomic position between the other two types. The diversity of morphological types in Neglectella suggests that further unknown species of this genus are likely to be discovered in the future. More collections and DNA sequence data will be needed in the future for this genus.Keywords：colony organization;Eremosphaeroideae;molecular phylogeny;Neglectella;Oocystaceae;pyrenoid4|0|1Updated：2023-05-20
Biology
- Abstract：Marine ranching can be regarded as a type of artificial fishery, and its construction aims at the sustainable utilisation of fishery resources. Therefore, the sustainable yield level of target species in marine ranching has become one of the concerns of stakeholders. The enhancement surplus production model proposed by Wang (2021) based on the traditional surplus production model can be used to assess the sustainable utilisation of settled species in marine ranches. However, when the target species has the characteristics of migration inside and outside marine ranches, its sustainability assessment will be affected. Based on the movement range and resource density levels of enhancement species inside and outside marine ranches, we built a biomass change model that is suitable for enhancement species with migration characteristics inside and outside marine ranches (migration enhancement biomass model). Moreover, we simulated the effects of factors, such as the ratio of the movement range and the ratio of resource density within and outside marine ranches and the fishing strategy for the enhancement species in marine ranches, on the estimation of maximum sustainable yield (MSY). Results show that the large movement range of enhancement species outside marine ranches was associated with the obvious advantage of the proposed migration enhancement model over the traditional enhancement production model. A small difference in the densities of enhancement species inside and outside marine ranches was highly beneficial for improving the accuracy of MSY estimation. The migration enhancement biomass model proposed in this study provides an idea for estimating the MSY of an enhancement species that migrates inside and outside marine ranches. Researchers can adjust the parameters of the model in accordance with the actual situation of resource distribution and changes to improve the scientificity of fishery stock assessment.Keywords：marine ranching;stock enhancement and releasing;migration;production model;maximum sustainable yield (MSY)4|2|0Updated：2023-05-20
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Aquaculture and Fisheries
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